1. Field
The present invention relates to an optical encoder, particularly to an optical encoder light shielding plate that turns or slides.
2. Related Art
Conventionally, for example, there is optical encoder light shielding plate 1 in which through-holes 3 are made in concentric with a center of turning shaft 2 as illustrated in FIG. 4. Light emitted from light source 4 and passes through through-hole 3 is detected by light receiving element 5, whereby a turning angle of turning shaft 2 is output as an output signal to a control device.
As to a method for producing the optical encoder light shielding plate, for example, Japanese Unexamined Patent Publication No. 2004-125734 discloses a method for producing a slit plate of an optical rotary encoder including a thin-film forming process of forming metallic thin films made of different metallic materials on both surfaces of a slit plate metallic base and a process of etching the metallic thin films and the metallic base to form a slit. In producing the slit plate, materials for the metallic thin films and the metallic base are selected such that an etching rate of the metallic thin film is lower than that of the metallic base.
However, in the optical rotary encoder slit plate producing method, the metallic thin films are formed on both the surfaces of the metallic base to obtain the slit plate having a three-layer structure. Therefore, production man-hours increase, and productivity is degraded.
Additionally, because the slit is formed by the etching process, it may be necessary to strictly perform time management in order to form the slit having high dimensional accuracy, and it takes time to produce the slit. Particularly, when the slit is formed by the etching process, a round surface is easily formed at an opening edge, and irregular reflection of the light is easily generated, which results in difficulty obtaining high measurement accuracy.